, 黄春玲, 陈旭中国地质大学（武汉）地球科学学院,武汉 430074
Sedimentary records of environmental changes of subalpine lakes: A case study of Yunzhong Lake in the southeastern Hubei province
PENGJia, HUANGChunling, CHENXu通讯作者:
收稿日期:2017-06-12
修回日期:2017-11-4
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版权声明:2018《地理研究》编辑部《地理研究》编辑部
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1 引言
湖泊是流域陆地和大气环境变化的敏感指示体[1],其中亚高山湖泊由于接近林线附近,气候的小幅波动会引起林线上下迁移,同时会伴随入湖营养盐、溶解有机碳等关键环境因子变化,加之亚高山湖泊中生物通常对光照、pH、温度等环境梯度耐受幅窄,气候小幅波动可能会引起湖泊生态系统的显著变迁[2]。同时,亚高山湖泊也是重要的生物多样性保护地和淡水资源储备地[3]。因此亚高山湖泊生态环境变化一直以来备受****关注[4,5,6]。例如在阿尔卑斯山中部的亚高山湖泊中,暖干气候延长湖泊换水周期,同时增强湖水-表层沉积物还原作用,沉积物中离子释放增加引起pH升高,进而偏碱性硅藻属种增加[4]。在北半球的高纬山地湖泊普遍存在自19世纪中叶以来Aulacoseira和Fragilaria属逐渐被Cyclotella属取代的现象,硅藻优势属种变化与全球变暖背景下水体垂直循环减弱相关[7]。可见,亚高山湖泊是研究全球变化的理想载体。欧盟自上世纪90年代投入大量经费成立高山湖泊研究专项（Mountain Lake Research,MOLAR）[8,9],专注于气候变化与人类活动干扰下的亚高山湖泊生态系统演化研究。近年来,国内****对亚高山湖泊生态环境演化关注度增加,尤其在青藏高原和云贵高原以及毗邻地区硅藻古生态学研究取得丰硕成果[10,11,12,13,14,15],例如在纳木错湖硅藻种群变化与水体的电导率相关[10];泸沽湖硅藻响应于夏季太阳辐射的变化[11]。目前已有的认识主要基于中国西南地区和青藏高原区的研究成果,相比而言,对中国东部地区亚热带亚高山湖泊的关注很少。
基于此,本文以鄂东南云中湖作为研究对象,该湖位于湖北省九宫山风景区核心地带,1958年筑坝蓄水形成人工水库,1984年大坝进一步扩建增高,库容125万m3,海拔1220 m,最大水深35 m。近年来由于九宫山旅游业快速发展,生活污水排放导致湖泊水质恶化,2009年湖中曾爆发蓝藻。由于缺乏长期的监测记录,目前对于湖泊环境变化的了解仅限于沉积物微量元素的记录,如表层沉积物V/Cr比值明显增加反映底层水体缺氧状态[16]。为进一步深入了解湖泊生态环境演化历史,本文综合沉积物硅藻、元素和粒度分析等,并结合流域气候和人类活动等历史资料,探讨气候变化以及人类活动影响下云中湖生态环境演化过程及其原因,以期为修复亚高山湖泊生态环境,改善流域水质提供参考。
2 研究方法与数据来源
2.1 研究区概况
云中湖位于湖北省咸宁市通山县九宫山自然保护区,如图1所示,其中心坐标为29°24′12″N、114°40′20″E,面积约20 hm2。云中湖地处亚热带季风性气候,年均气温14.3 ℃,年均降雨量1537 mm,所属流域为富水河流域,地形山丘盆地参差分布,流域内母岩为花岗岩,土壤以黄棕壤为主,植被为以马尾松、青冈栎和毛栗为主要优势种的针阔混交林。
显示原图|下载原图ZIP|生成PPT图1云中湖采样点位置图
-->Fig. 1Location of the sampling point in Yunzhong Lake
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20世纪50年代以来,由于该区开始修建水库和宾馆,原始植被遭受破坏,马尾松入侵并逐渐增加[17]。该湖在旅游、饮用水供给、发电和灌溉等方面发挥重要的生态服务功能。流域周围建筑凌乱,房地产开发频繁,常年接受沿湖周围七十余家宾馆、招待所以及疗养院未经处理排放的污水,年纳污水量在14万t左右[18]。
2.2 样品采集及鉴定
2014年4月,利用重力采样设备在九宫山云中湖的湖区中心附近（29°24'20"N、114°40'4"E）采集长为27 cm的柱状沉积岩芯,现场对沉积岩芯按间隔1 cm进行分样,共得到27个样品,密封保存后带回实验室后置于4 ℃的冰箱中冷藏以备分析测试。210Pb比活度采用美国EG&GOrtec公司生产的锗井型探测器（HPGe GWL-120-15）进行测定,测试间隔为2 cm。其中210Pb标准样品由英国利物浦大学提供,226Ra标准样品由中国原子能科学研究院提供,测试误差小于10%。TN和TOC采用EA3000型元素分析仪测定（精度为0.1%）,由TN与TOC对应的比值得到C/N比值数据,TP、K、Ca、Na、Mg、Al、Zn、Fe、Pb、Cu、Mn、Li、Cr用等离子体原子发射光谱仪（ICP-AES）测定,仪器精度控制在重复测量误差小于±5%。元素样品测试间隔为2cm。沉积物粒度经过10%双氧水处理后,用Mastersize-2000激光粒度仪测定,输出中值粒径等参数。
沉积硅藻采用标准方法处理[19],即对每份样品分别取约0.5 g,用10%HCl和30%H2O2依次去除碳酸盐和有机质组分,随后用蒸馏水进行三次清洗,最后取0.5 ml使用加拿大树胶制成玻片。硅藻样品分析间隔为1 cm。硅藻鉴定参照Krammer和Lange-Bertalot的分类系统[20],在Olympus CX31显微镜下1000倍鉴定统计,每个样品硅藻壳体统计以500粒为基数,属种丰度用百分比表示。
2.3 气象资料来源
由于缺乏实测的气象数据资料,云中湖夏季降雨量、年均距平温度数据均来自荷兰皇家气象研究所（KNMI）网站（http://climexp.knmi.nl/selectfield_obs.cgi）,选择区域位置在29°~30°E、114°~115°N的数据代表研究区气候。2.4 数据分析
主成分分析（Principal Component Analysis,PCA）能将多个变量转化为少数几个综合变量,是一种线性统计方法[21]。采用Past 3.0软件对沉积物12种元素（K、Ca、Na、Mg、Al、Zn、Fe、Pb、Cu、Mn、Li和Cr）组成进行主成分分析。在此基础上,计算化学蚀变指数（Chemical Index of Alteration,CIA）以反映流域的风化程度[22],具体计算公式为[22]：CIA=[Al2O3/(Al2O3+CaO+Na2O+K2O)]×100 （1）
硅藻数据保留至少在两个以上样品中出现,且其中一个样品超过2%的主要硅藻属种（15种）,用于后续统计分析。采用地层约束聚类法（Stratigraphically Constrained Cluster analysis）划分硅藻组合变化的主要阶段,聚类分析在Tilia软件在中执行[23]。采用降维对应分析（Detrended Correspondence Analysis,DCA）揭示硅藻种群组合变化的主要特征。DCA分析结果显示第一轴的长度为0.954个标准单位,所以采用线性模型—冗余分析（Redundancy analysis,RDA）进一步揭示硅藻与解释变量之间的关系[24]。冗余分析以硅藻数据作为响应变量,沉积物元素（K、Ca、Na、Mg、Al、Zn、Fe、Pb、Cu、Mn、Li、Cr、TN、TOC、TP）以及气候因子（夏季降水量和年距平温度）作为解释变量。夏季降水量和温度采用3点滑动平均处理。在进行冗余分析之前,对解释变量进行对数转换（除年距平温度外）基于蒙特卡洛置换检验（P<0.05;n=499非限制性置换）逐步预选筛选出解释硅藻组合演替的显著因子。DCA和RDA在CANOCO 4.5软件中进行。
3 结果分析
3.1 沉积年代序列
云中湖沉积岩芯中的210Pb比活度除表层样品中略有下降外,基本呈指数递减趋势（图2）,表明210Pb沉积后受到扰动较少。综合考虑到岩芯底部210Pb与226Ra未达到衰变平衡、缺乏独立的时标（137Cs比活度峰值不明显,本文未显示）等因素,本文选用恒定沉积通量模式（constant initial concentration,CIC）计算年代,CIC模式是在210Pb输入通量与沉积物堆积速率恒定条件下计算年代的方法,适用于沉积物主要来源于表层侵蚀产物,210Pb含量明显受物源影响的情况[25]。计年公式为[25]：式中：t为沉积物年代;C(0)、C(h)分别为沉积物表层和深度为h处210Pb比活度;λ为衰变常数,取0.0311 a-1。
显示原图|下载原图ZIP|生成PPT图2云中湖沉积岩芯中210Pb比活度随深度变化
-->Fig. 2Changes of 210Pb activities with depth in sedimentary core of Yunzhong Lake
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由210Pb实测数据（图2）,得到云中湖沉积物210Pb比活度（x）与深度（y）的拟合曲线为y=-15.7ln(x)+107.68,R2=0.94,由此推出沉积物平均沉积速率为0.4867 cm·a-1,沉积物27 cm处年代在1958年左右,与建坝时间一致。
3.2 沉积硅藻组合
在沉积岩芯中共鉴定硅藻25属87种：浮游种类以Aulacoseira属和Cyclotella属占优势,包括Aulacoseira alpigena、Aulacoseira ambigua、Cyclotella pseudostelligera、Cyclotella stelligera和Cyclostephanos dubius;Fragilaria nanana和Asterionella formosa也较为常见;底栖种类以Achnanthes minutissima为主。CONISS聚类分析结果显示（图3）,硅藻组合可以划分出2个组合带,每个组合带又细化为2个组合亚带,具体的变化特征如下：组合带I（27~10 cm,1958-1993年）：A. minutissima、A. alpigena、A. ambigua和F. nanana为主要优势属种,平均含量分别为37.3%、10%、13.4%和11.8%;A. formosa、C. stelligera、Navicula cryptotenella也较为常见,平均含量分别为7.3%、4.4%和3.4%;Fragilaria capucina、C. dubius、Cyclotella bodanica、Navicula pupula零星出现。
显示原图|下载原图ZIP|生成PPT图3云中湖沉积岩芯中主要硅藻属种图谱
-->Fig. 3Diatom diagram of main species in the sedimentary core of Yunzhong Lake
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亚带Ia（27~16 cm）：A. formosa含量从底部26%快速下降至5%以下;与之相反,A. alpigena迅速增加至20%以上,在该亚带顶部含量有所回落。此外,A. minutissima和A. ambigua含量稳定呈小幅波动变化;其他属种含量变化很小。亚带Ib（16~10 cm）：A. minutissima含量明显升高并维持35%以上,平均含量较Ia亚带升高14%;相应的A. alpigena和A. ambigua含量降低。值得注意的是,C. pseudostelligera明显增加,尽管平均含量不超过10%。
组合带II（10~0 cm,1993-2013年）：A. minutissima和F. nanana优势度降低,而Cyclotella属和Aulacoseira属含量有明显升高。总体而言,底栖种类整体含量明显减少,相应的浮游种类含量增加。
亚带IIa（10~5 cm）：A. minutissima含量迅速降低,在该亚带一直低于5%平均含量较Ib亚带减少20%以上,A. alpigena含量在该亚带也明显减少,一直低于5%。与此相反的是C. pseudostelligera、A. ambigua和N. cryptotenella含量都有不同程度上升。亚带IIb（5~0 cm）：最显著变化为A. alpigena含量快速升高并维持高值,尽管在顶部有所回落;而A. minutissima和F. nanana含量持续降低,C. bodanica含量较IIa亚带明显升高。
3.3 元素含量变化
根据12种元素的垂向分布特征（图4）,结合测年数据以及硅藻组合带划分,元素组合变化特征如下：硅藻组合Ia亚带（27~16 cm,1958-1981年）：Pb、Zn含量下降并在21 cm处达到谷值,随后迅速升高,但没有超过初始含量;Cu含量在19 cm出现一个峰值,整体有上升趋势;Na含量有起伏,整体上变化不大;其余元素变化不明显。
显示原图|下载原图ZIP|生成PPT图4云中湖沉积岩芯中元素含量随深度的变化
-->Fig. 4Variation of element content with the depth in the sedimentary core of Yunzhong Lake
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Ib亚带（16~10 cm,1981-1993年）：大部分元素含量先升高再减少,在13 cm前后有一高值,此后呈回落态势。其他元素中,Mn含量在15 cm前后达到峰值,随后下降,K含量呈上升趋势,Zn、Al、Li含量呈下降趋势。
IIa亚带（10~5 cm,1993-2004年）：除Zn以外的所有元素含量都呈下降趋势,而Zn含量升高到7 cm峰值后下降。
IIb亚带（5~0 cm,2004-2013年）：大部分元素含量先升高在3 cm处达到峰值后下降;Na、Ca、Zn含量在3 cm处为谷值,接着快速上升;Mn含量一直处于上升趋势。
3.4 数值分析
元素的PCA第一与第二主成分分别解释元素数据方差的61.9%和22.7%,硅藻属种的DCA第一轴与第二轴分别解释了硅藻属种数据方差的32.8%和10.1%。图5显示了PCA和DCA结果与中值粒度、CIA指数、夏季降雨量、年均距平温度、TP、TOC、TN含量、Fe/Mn和C/N比值的综合对比结果。元素PCA第一主成分先升高后降低,而第二主成分则为先缓慢下降,在2004年降至最低后回升;硅藻DCA第一轴得分波动下降,而第二轴得分在1981年以前波动下降,之后逐渐升高,1996年后回落;中值粒径总体变幅不大,近在1988年附近存在一明显峰值;CIA与TP相似,在1983年以前相对稳定,1983-1996年相对较低,此后小幅上升;夏季降雨量则是先波动上升,在1998年后下降,又在2008年后小幅升高;年均距平温度、TN与TOC变化基本一致,整体呈波动升高趋势;C/N比值除在1980s有小幅升高外总体呈下降趋势。Fe/Mn除了在1983年和表层样品中有两处低值以外,总体升高。
显示原图|下载原图ZIP|生成PPT图5沉积物多指标与当地气候数据对比
-->Fig. 5Comparison between sedimentary multi-proxy records and local climatic data
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RDA结果显示,前两轴共同解释了硅藻组合方差的40.2%,Al、Fe、Pb和年均距平温度是解释硅藻组合变化的四个显著因子（图6）。组合带I（1958-1993年）样品中Al、Fe元素含量相对较高,浮游类硅藻与Al、Fe元素变化呈正相关,如F. nanana和A. formosa;组合带II（1993-2013年）样品对应于温度升高和Al、Fe和Pb元素含量低值。
显示原图|下载原图ZIP|生成PPT图6RDA分析结果
-->Fig. 6The results of RDA analysis
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4 讨论
云中湖浅孔岩芯多指标记录揭示了近60年来湖泊生态环境演化历史,硅藻组合中以浮游类型（如Aulacoseira和Cyclotella属）和附生类型（如Achnanthes和Fragilaria属）共占优势,这反映进入沉积物之前不同生境的硅藻壳体在水体中的混合作用。1993年前后硅藻组合由Achnanthes-Aulacoseira-Fragilaria优势组合向Aulacoseira-Cyclotella-Achnanthes优势组合转变,反映湖泊生态环境在上世纪90年代发生显著变化。结合多指标记录,对生态环境变化过程及原因分析如下。4.1 硅藻组合变化与流域风化过程
云中湖水库建成初期会造成库区周边植被破坏,CIA指数在80~85指示温暖湿润气候下的中等风化强度[22],侵蚀入湖的Al、Fe和Pb量大,同时入湖的氮磷营养元素丰富[26],在此背景下,偏好碱性、营养丰富水体的硅藻属种大量生长,如A. formosa喜欢在氮、磷、碳和钙供给丰富的水体生长[27],F. nanana在西伯利亚地区电导率高的湖泊中大量出现,且Fragilaria属常在冰川消退后湖泊形成初期高碱性水体中大量出现[28],A. minutissima在英格兰和苏格兰地区营养丰富、pH相对较高的水体中优势明显[29]。因此,从硅藻优势组合和元素含量可以判识,水库建成初期水体偏碱性且氮、磷等营养物质丰富,这主要与流域开垦初期,风化作用带来物源输入较多相关。随着流域植被逐渐恢复,沉积物TOC小幅升高指示入湖的有机碳增加,这可能导致水体透光性减弱和pH的略微降低,从而促进A. alpigena快速增加,该种在溶解有机碳含量高、弱酸性低光照的湖泊中常见[30]。1958-1981年以A. minutissima占优势的硅藻组合以及高CIA指数,与流域较强的风化状态相对应。1984年云中湖水库在原坝下游100 m处修建新坝（图1）,新坝修建所需石材主要来自周围山体,石材采挖过程中产生大量碎屑颗粒。加之,周围大量宾馆修建对地表原始植被破坏,坡面流水侵蚀作用增强,进而将碎屑颗粒带入湖盆。这一时期CIA指数的下降和中值粒径增粗指示了风化相对较弱的粗颗粒碎屑入湖。新坝修建后湖泊水位抬升,滨岸带范围扩大,这扩充了以A. minutissima作为代表的附生种生境[31],加之水库汇水面积增加,溪流带入的A. minutissima可能也随之增加,因而A. minutissima成为此时主要优势种。同时在湖泊水体变深,并且风速降低的情况下水体扰动减弱[32],生存于扰动较强水体的Aulacoseira属含量减少[33],而适宜水动力较弱环境的薄壳浮游种C. pseudostelligera含量则出现明显增加[34]。总体而言,1993年之前云中湖硅藻组合变化主要与建坝初期气候调控下的流域侵蚀过程相关。
4.2 硅藻组合变化与湖泊富营养化
1993年以来适应中—富营养水体的硅藻（如C. pseudostelligera）明显增加,这与该时期沉积物总磷和总氮持续升高以及增温相对应。CIA相对稳定反映此时流域风化强度变化不大。这一时期硅藻组合的变化与温度呈现明显正相关,暗示气候变暖是硅藻组合变化的重要驱动力,温度升高促进了湖泊内源营养的释放[35],沉积物C/N降低且低于10反映湖泊有机质中藻类生产力贡献增加。值得注意的是,增温过程与氮磷输入增长同步,20世纪90年代中后期当地旅游业快速发展,生活污水排放导致外源营养物质输入增加[35],因而外源营养的大量输入是此时硅藻组合变化的潜在影响因子,水体营养富集最终促进了中—富营养属种的增殖。沉积物有机质大量累积,可能是金属元素在这一时期相对下降的原因。徐俏等基于沉积物微量元素分析发现,20世纪90年代以来,V/Cr大于2且呈升高态势,指示湖泊底层水体逐渐趋于缺氧状态[16]。同时2004年以来,云中湖夏季蓝藻时有爆发,Fe/Mn比值降低,也指示了湖泊沉积物—水体界面由氧化状态向还原状态的转变[36]。A. alpigena自2006年以来迅速上升并维持在较高值,该种在长江中下游湖泊中TP的适宜值为130 μg/L[37],为典型耐营养种,其优势增大反映湖泊营养富集加剧,这可能是自2008年九宫山被列为国家4A级景区以来,云中湖周边宾馆业快速发展,年均大约14万t污水倾倒入湖加剧湖泊富营养化[16],进而使得耐营养属种逐渐占据优势地位[15]。相比而言,适合中营养水体属种A. minutissima（该种在长江中下游湖泊中总磷最适值为56 μg/L[37]）受过高营养限制而减少。营养富集导致藻类增殖,由于藻类分解过程中水体溶解氧大量消耗导致底层水体缺氧,缺氧还原条件会促进沉积物磷释放[36],由此产生营养富集的正反馈效应将增加湖泊生态修复的难度。5 结论
云中湖沉积岩芯揭示了1958年以来云中湖的生态环境演化过程：1958-1993年间建坝初期,硅藻组合变化主要响应气候变化调控下的流域侵蚀过程;1993年以来中—富营养种硅藻增多主要响应于气候变暖和旅游发展导致的入湖污染增加。A. alpigena等耐营养种大量出现反映云中湖生态环境有恶化趋势,因此必须采取有效环境保护措施（如污水治理）以保护这一珍贵的水源地和旅游景点。本文揭示了气候变化和人类活动干扰下的亚热带亚高山湖泊生态环境演化过程,并为九宫山云中湖生态环境保护提供科学基础。致谢：中南民族大学资源与环境学院的曹艳敏博士协助野外采样,谨致谢忱。
The authors have declared that no competing interests exist.
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| [1] | . Recent advances in our understanding of the importance of continental- to global-scale connectivity among terrestrial and aquatic ecosystems make consideration of aquatic-terrestrial linkages an urgent ecological and environmental issue. Here, we describe the role of inland waters as sentinels and integrators of the impact of humans on terrestrial and aquatic ecosystems. The metabolic responses of lakes and streams (ie the rates at which these systems process carbon) are proposed as a common metric to integrate the impacts of environmental change across a broad range of landscapes. Lakes and streams transport and alter nutrients, contaminants, and energy, and store signals of environmental change from local to continental scales over periods ranging from weeks to millennia. A carefully conceived and well-integrated network that includes monitoring and experimental approaches to terrestrial-aquatic connectivity is critical to an understanding of basic ecosystem-level processes and to forecasting and mitigating future environmental impacts at the continental scale. |
| [2] | . |
| [3] | . <br /><div>We report the results of a study on modern zooplankton community as well as on Cladocera sub-fossil remains from 15 high altitude lakes in the Italian Central-Southern Alps, aimed at investigating changes after 19th Century industrialisation. Present-day communities were compared to those of the pre-industrial period (approximately pre-1850 AD). Numerical analysis suggests a relationship between environmental variables, such as pH or total phosphorus, and the cladoceran community structure. However, as found in previous studies, another important environmental variable not included in numerical analysis, is presence or absence of fish. Arctodiaptomus alpinus was not found at pH levels lower than 6.21, while Daphnia lacked from lakes where fish were regularly introduced. Daphnia re-colonised the today fish-less Lago Paione Inferiore, whereas in the past, with a regular introduction of fish, only rotifers and a few Cyclops were found. The re-colonisation is interpreted by regarding the three Paione lakes as parts of a cascade system, where a transport from the upper Lago Paione Superiore to the lower Lago Paione Inferiore can take place, and the sediments represent a kind of an "egg bank". |
| [4] | . DESPITE the attention given in recent years to the issue of lake acidification by anthropogenic emissions, the question of how climate change might influence the acid-base equilibria of lakes has been little explored. Here we use palaeolimnological data to show that the acidity of two soft-water, high-altitude lakes in the central Alps was correlated with regional temperature during the entire nineteenth century, colder years being associated with lower pH. Our findings of high concentrations of organic matter and elevated Fe/Mn ratios in the corresponding sediment layers support the view that this relationship is dictated primarily by the temperature dependence of in-lake processes of alkalinity generation. The onset of anthropogenically derived acid precipitation at the beginning of the present century led to a breakdown of the pH-temperature relationship, with pH dropping steadily to values of 5.6-5.8. Nevertheless, temperature maxima around 1950 still coincide with peaks in pH and some pH minima before 1900 fell as low as as the levels around 1970. It is an open question whether the very recent levelling off that we observe in the decline of pH is due to rising temperatures or to decreasing precipitation acidity. |
| [5] | . Abstract Fifty-five paleolimnological records from lakes in the circumpolar Arctic reveal widespread species changes and ecological reorganizations in algae and invertebrate communities since approximately anno Domini 1850. The remoteness of these sites, coupled with the ecological characteristics of taxa involved, indicate that changes are primarily driven by climate warming through lengthening of the summer growing season and related limnological changes. The widespread distribution and similar character of these changes indicate that the opportunity to study arctic ecosystems unaffected by human influences may have disappeared. |
| [6] | . Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance.To date, there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on time-scales from decades to millions of years.We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners.The integration of online participation, both before and during the workshop, increased international engagement in question selection.The questions selected are structured around six themes: human nvironment interactions in the Anthropocene; biodiversity, conservation and novel ecosystems; biodiversity over long time-scales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology.Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes and the continued application of long-term data for better-informed landscape management.Synthesis. Palaeoecology is a vibrant and thriving discipline, and these 50 priority questions highlight its potential for addressing both pure (e.g. ecological and evolutionary, methodological) and applied (e.g. environmental and conservation) issues related to ecological science and global change. |
| [7] | . Abstract A synthesis of over 200 diatom-based paleolimnological records from nonacidified/nonenriched lakes reveals remarkably similar taxon-specific shifts across the Northern Hemisphere since the 19th century. Our data indicate that these diatom shifts occurred in conjunction with changes in freshwater habitat structure and quality, which, in turn, we link to hemispheric warming trends. Significant increases in the relative abundances of planktonic Cyclotella taxa ( P <0.01) were concurrent with sharp declines in both heavily silicified Aulacoseira taxa ( P <0.01) and benthic Fragilaria taxa ( P <0.01). We demonstrate that this trend is not limited to Arctic and alpine environments, but that lakes at temperate latitudes are now showing similar ecological changes. As expected, the onset of biological responses to warming occurred significantly earlier ( P <0.05) in climatically sensitive Arctic regions (median age= ad 1870) compared with temperate regions (median age= ad 1970). In a detailed paleolimnological case study, we report strong relationships ( P <0.005) between sedimentary diatom data from Whitefish Bay, Lake of the Woods (Ontario, Canada), and long-term changes in air temperature and ice-out records. Other potential environmental factors, such as atmospheric nitrogen deposition, could not explain our observations. These data provide clear evidence that unparalleled warming over the last few decades resulted in substantial increases in the length of the ice-free period that, similar to 19th century changes in high-latitude lakes, likely triggered a reorganization of diatom community composition. We show that many nonacidified, nutrient-poor, freshwater ecosystems throughout the Northern Hemisphere have crossed important climatically induced ecological thresholds. These findings are worrisome, as the ecological changes that we report at both mid- and high-latitude sites have occurred with increases in mean annual air temperature that are less than half of what is projected for these regions over the next half century. |
| [8] | . In the framework of the Mountain Lake Research (MOLAR) project, the water chemistry of 23 lakes covering Europe from the Svalbard Islands to the South of Spain were studied. The lakes are located above or beyond the timber line in the most important mountain areas in Europe. Atmospheric deposition was sampled at 11 sites, representative of different lake districts. 24 institutions took part in the activity. The comparability of the analytical results performed in 18 laboratories was assured by strict sampling and analysis protocols and by a detailed programme of Analytical Quality Assessment/Control. The paper summarises the main morphometric and hydrological characteristics of the lakes and their watersheds and discusses the results of the atmospheric deposition and lake water chemistry. An overview on the main processes controlling the composition and ionic ratio of deposition and lake chemistry is given. |
| [9] | . |
| [10] | . Paleolimnological analyses can be used to evaluate limnological responses to changing climate over decadal to centennial timescales, especially in regions with sparse lake monitoring data. We used a training set with 90 lakes to develop a diatom-based conductivity transfer function and address climate-driven changes in lakes on the Qinghai-Xizang Plateau, Tibet. This new training set is an expanded version of a previous model (Yang et al. in J Paleolimnol 30:1 19, 2003 ) and shows improved performance statistics for the conductivity model. The expanded training set also contains diatom species not previously identified from the region, such as Stephanodiscus sp. and Cyclotella sp., which are common eutrophic indicator species in other regions, but can also be influenced by water column conductivity. The new conductivity transfer function was applied to Lakes Nam Co and Chen Co in Tibet. Recent conductivity inferences were compared with climate data from the Dangxiong weather station and water level records from Yangzhuyong Co, which show increasing temperature and lower water levels, respectively, since AD 1960. Other studies showed that the water balance for many lakes on the Qinghai-Xizang Plateau is complex, affected by both evaporation and glacial melting. Our paleolimnological reconstructions, which include sediment particle size data, indicate that over relatively short timescales glacial meltwater can influence lake hydrology, but over decadal timescales, increases in evaporation, driven by rising temperatures, dominate. Our findings suggest that regional warming is lowering water levels at these sites and will continue to do so given predicted future climate warming. |
| [11] | . 中国科学院机构知识库(中国科学院机构知识库网格（CAS IR GRID）)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。 |
| [12] | . The south-east margin of Tibet is highly sensitive to global environmental change pressures, in particular, high contemporary reactive nitrogen (Nr) deposition rates (ca. 40 kg ha 1 yr 1), but the extent and timescale of recent ecological change is not well prescribed. Multiproxy analyses (diatoms, pigments and geochemistry) of 210Pb-dated sediment cores from two alpine lakes in Sichuan were used to assess whether they have undergone ecological change comparable to those in Europe and North America over the last two centuries. The study lakes have contrasting catchment-to-lake ratios and vegetation cover: Shade Co has a relatively larger catchment and denser alpine shrub than Moon Lake. Both lakes exhibited unambiguous increasing production since the late 19th to early 20th. Principle component analysis was used to summarize the trends of diatom and pigment data after the little ice age (LIA). There was strong linear change in biological proxies at both lakes, which were not consistent with regional temperature, suggesting that climate is not the primary driver of ecological change. The multiproxy analysis indicated an indirect ecological response to Nr deposition at Shade Co mediated through catchment processes since ca. 1930, while ecological change at Moon Lake started earlier (ca. 1880) and was more directly related to Nr deposition (depleted 15N). The only pronounced climate effect was evidenced by changes during the LIA when photoautotrophic groups shifted dramatically at Shade Co (a 4-fold increase in lutein concentration) and planktonic diatom abundance declined at both sites because of longer ice cover. The substantial increases in aquatic production over the last ca. 100 years required a substantial nutrient subsidy and the geochemical data point to a major role for Nr deposition although dust cannot be excluded. The study also highlights the importance of lake and catchment morphology for determining the response of alpine lakes to recent global environmental forcing. |
| [13] | . 目前国内对生产力-生物多样性关系(productivity-diversity relationship, PDR)的研究主要集中于陆地生态系统和空间尺度，少量关于湖泊系统的研究也主要集中于现代调查，缺乏较长时间尺度上的模式探讨。本文应用沉积物色素记录首先重建了抚仙湖和滇池初级生产力变化历史，对硅藻群落的主成分分析(PCA)表明湖泊初级生产力是驱动硅藻群落变化的主要环境梯度(PCA第一主轴得分)。进一步分析硅藻群落α与β多样性响应湖泊生产力水平的模式，发现滇池硅藻群落表现为随着系统生产力的上升物种丰度减少、β多样性降低，而抚仙湖呈现相反的变化模式。而且两个湖泊β多样性与生产力平均水平的关系均表现出与α多样性相似的特征；但在与生产力变化幅度的关系上，滇池表现出显著的负相关，而抚仙湖则没有显著的变化。滇池硅藻群落生产力随硅藻多样性的降低显著增加(R2 = 0.597, P < 0.01)，而在抚仙湖无显著变化，表明了滇池群落多样性的维持作用对群落生产力的影响较弱(如与营养盐富集的促进作用相比)。滇池明显的富营养化过程与强烈的人类扰动带来的环境异质性降低可能对群落多样性-生产力的关系产生了明显的控制作用。 . 目前国内对生产力-生物多样性关系(productivity-diversity relationship, PDR)的研究主要集中于陆地生态系统和空间尺度，少量关于湖泊系统的研究也主要集中于现代调查，缺乏较长时间尺度上的模式探讨。本文应用沉积物色素记录首先重建了抚仙湖和滇池初级生产力变化历史，对硅藻群落的主成分分析(PCA)表明湖泊初级生产力是驱动硅藻群落变化的主要环境梯度(PCA第一主轴得分)。进一步分析硅藻群落α与β多样性响应湖泊生产力水平的模式，发现滇池硅藻群落表现为随着系统生产力的上升物种丰度减少、β多样性降低，而抚仙湖呈现相反的变化模式。而且两个湖泊β多样性与生产力平均水平的关系均表现出与α多样性相似的特征；但在与生产力变化幅度的关系上，滇池表现出显著的负相关，而抚仙湖则没有显著的变化。滇池硅藻群落生产力随硅藻多样性的降低显著增加(R2 = 0.597, P < 0.01)，而在抚仙湖无显著变化，表明了滇池群落多样性的维持作用对群落生产力的影响较弱(如与营养盐富集的促进作用相比)。滇池明显的富营养化过程与强烈的人类扰动带来的环境异质性降低可能对群落多样性-生产力的关系产生了明显的控制作用。 |
| [14] | . 随着人类活动的增强与全球气候变暖的持续,近年来云南湖泊的生态系统功能持续退化,而目前对云南湖泊生态系统的研究还主要集中于单一环境压力的生态效应。以星云湖为研究对象,通过沉积物记录与现代监测资料,识别在湖泊富营养化、气候变化以及人类强烈干扰下硅藻群落结构响应的过程,并甄别驱动群落变化的主要环境压力及其强度。结果显示随着湖泊生产力水平(如沉积物叶绿素a浓度)的增加,硅藻物种组成发生了明显的变化,主成分分析表明了水体富营养化是驱动群落变化的主要环境因子(<i>r</i>=-0.63, <i>P</i>< 0.001)。简约模型与方差分解的结果表明近200年来(钻孔长度38cm),湖泊营养水平和水动力是驱动星云湖硅藻群落变化的主要环境因子,分别解释了群落变化的18.8%和2.9%;而1951年以后,湖泊营养水平和温度分别解释了硅藻群落结构变化的31.4%和26.8%。研究结果表明了硅藻群落长期变化的主控因子是湖泊营养水平,而人类活动及气候变化等可以通过改变湖泊水动力及湖水温度来驱动硅藻群落的演替,同时抚仙湖-星云湖的连通性也对硅藻群落的演替产生了一定影响。 . 随着人类活动的增强与全球气候变暖的持续,近年来云南湖泊的生态系统功能持续退化,而目前对云南湖泊生态系统的研究还主要集中于单一环境压力的生态效应。以星云湖为研究对象,通过沉积物记录与现代监测资料,识别在湖泊富营养化、气候变化以及人类强烈干扰下硅藻群落结构响应的过程,并甄别驱动群落变化的主要环境压力及其强度。结果显示随着湖泊生产力水平(如沉积物叶绿素a浓度)的增加,硅藻物种组成发生了明显的变化,主成分分析表明了水体富营养化是驱动群落变化的主要环境因子(<i>r</i>=-0.63, <i>P</i>< 0.001)。简约模型与方差分解的结果表明近200年来(钻孔长度38cm),湖泊营养水平和水动力是驱动星云湖硅藻群落变化的主要环境因子,分别解释了群落变化的18.8%和2.9%;而1951年以后,湖泊营养水平和温度分别解释了硅藻群落结构变化的31.4%和26.8%。研究结果表明了硅藻群落长期变化的主控因子是湖泊营养水平,而人类活动及气候变化等可以通过改变湖泊水动力及湖水温度来驱动硅藻群落的演替,同时抚仙湖-星云湖的连通性也对硅藻群落的演替产生了一定影响。 |
| [15] | . . |
| [16] | . 近年来湖北省通山县九宫山风景区的云中湖污染日益严重,已引起诸多关注,然而目前并不清楚该湖生态环境变化轨迹以及原因.通过对云中湖沉积物年代学、微量元素、有机碳和粒度分析,结合聚类分析和地质累积指数等方法,揭示近50 a云中湖环境变化历史.结果表明,云中湖沉积物中14种微量元素含量随深度呈相似的变化趋势,且两两之间呈显著正相关关系,反映元素输入物源的一致性.在20世纪80年代前,湖底沉积物中微量元素含量变化很小,表明流域环境变化较小,20世纪80年代以来微量元素含量呈波动变化,其中在10和4 cm深度出现2次明显低值,下部低值与沉积物粒度增粗相对应,这可能是由于气候和人为旅游开发原因所致;顶部低值与有机碳含量增加相一致,反映了水体富营养化过程以及有机质输入对沉积元素的稀释作用.1993年以来元素V/Cr比值明显增加并超过2.0,反映底层水体向缺氧状态转变.各元素的地质累积指数小于0.5,表明云中湖重金属污染程度处于较轻水平.综合分析云中湖沉积物研究记录可知,20世纪90年代之前云中湖湖泊环境相对稳定,20世纪90年代以后流域环境发生明显变化,水体环境呈恶化趋势. . 近年来湖北省通山县九宫山风景区的云中湖污染日益严重,已引起诸多关注,然而目前并不清楚该湖生态环境变化轨迹以及原因.通过对云中湖沉积物年代学、微量元素、有机碳和粒度分析,结合聚类分析和地质累积指数等方法,揭示近50 a云中湖环境变化历史.结果表明,云中湖沉积物中14种微量元素含量随深度呈相似的变化趋势,且两两之间呈显著正相关关系,反映元素输入物源的一致性.在20世纪80年代前,湖底沉积物中微量元素含量变化很小,表明流域环境变化较小,20世纪80年代以来微量元素含量呈波动变化,其中在10和4 cm深度出现2次明显低值,下部低值与沉积物粒度增粗相对应,这可能是由于气候和人为旅游开发原因所致;顶部低值与有机碳含量增加相一致,反映了水体富营养化过程以及有机质输入对沉积元素的稀释作用.1993年以来元素V/Cr比值明显增加并超过2.0,反映底层水体向缺氧状态转变.各元素的地质累积指数小于0.5,表明云中湖重金属污染程度处于较轻水平.综合分析云中湖沉积物研究记录可知,20世纪90年代之前云中湖湖泊环境相对稳定,20世纪90年代以后流域环境发生明显变化,水体环境呈恶化趋势. |
| [17] | . 九宫山自然保护区位于中国中亚热带向北亚热带过渡区,植被构成以 森林植被为主.通过调查和分析,将九宫山自然保护区植被划分为5个植被型组,11个植被型,32个群系.九宫山自然保护区的种子植物区系分布中温带性质和 热带性质的属分别为384和302属;植被类型中主要森林植被的构成为:暖温性、温性和寒温性针叶林群系数目依次是1、1、0,常绿阔叶林、落叶常绿阔叶 混交林和落叶阔叶林群系数目分别为3、7、7;森林植被中落叶常绿阔叶混交林的分布面积最大.与井冈山自然保护区、庐山、后河自然保护区、清凉峰自然保护 区、神农架自然保护区以及董寨鸟类自然保护区等地植被相关特征的比较分析表明,该区植被种子植物的主要组成种类以及森林植被类型和分布等具有明显的地带性 过渡特征. . 九宫山自然保护区位于中国中亚热带向北亚热带过渡区,植被构成以 森林植被为主.通过调查和分析,将九宫山自然保护区植被划分为5个植被型组,11个植被型,32个群系.九宫山自然保护区的种子植物区系分布中温带性质和 热带性质的属分别为384和302属;植被类型中主要森林植被的构成为:暖温性、温性和寒温性针叶林群系数目依次是1、1、0,常绿阔叶林、落叶常绿阔叶 混交林和落叶阔叶林群系数目分别为3、7、7;森林植被中落叶常绿阔叶混交林的分布面积最大.与井冈山自然保护区、庐山、后河自然保护区、清凉峰自然保护 区、神农架自然保护区以及董寨鸟类自然保护区等地植被相关特征的比较分析表明,该区植被种子植物的主要组成种类以及森林植被类型和分布等具有明显的地带性 过渡特征. |
| [18] | . . |
| [19] | . In: Smol J P, Birks H J B, Last W M, et al. |
| [20] | . In: Ettl H, Gerloff J, Heynig H, et al., et al. |
| [21] | |
| [22] | . The early Proterozoic Huronian Supergroup of the north shore of Lake Huron (Fig. 1) is a thick (up to 12,000 m) succession of sedimentary and volcanic rocks deposited between about 2,500 and 2,100 Myr ago 1 . Here we present a palaeoclimatic interpretation of the Huronian based on approximately 200 major elements analyses of lutites. Most of these are new analyses from the Gowganda and Serpent Formations (Fig. 2). The remainder are from published sources cited in Fig. 4. The composition of lutites from the Huronian Supergroup records an early period of intense, probably tropical, weathering followed by climatic deterioration that culminated in widespread deposition of glaciogenic sediments of the Gowganda Formation. Climatic amelioration followed during deposition of the succeeding Huronian formations. The Huronian succession can be interpreted using a uniformitarian approach in that present day seafloor spreading rates and latitude-related climatic variations are compatible with available geochronological and palaeomagnetic data. |
| [23] | . Stratigraphically constrained cluster analysis is a multivariate method for quantitative definition of stratigraphic zones. As opposed to ordinary, unconstrained cluster analysis, only stratigraphically adjacent clusters are considered for merging. The method of incremental sum of squares has been used widely for unconstrained analyses and has proved particularly satisfactory for pollen frequency data. CONISS is a FORTRAN 77 program for stratigraphically constrained cluster analysis by this method. Several data transformations lead to different implicit dissimilarity coefficients. As an option, the program also will perform an unconstrained analysis, which can be useful for comparison with the constrained analysis. |
| [24] | . . |
| [25] | . 采用放射性核素^137Cs和^210Pb计年法测定百年来湖北网湖沉积物的年代，据此计算 出网湖的沉积速率．结果表明：2种计年方法测得的沉积速率基本一致，以1954年和1963年为时标，^137Cs测得的沉积速率分别为 0．594cm·a^-1和0．557cm·a^-1。^210Pb计年法CIC模式计算得到网湖平均沉积速率为0．56cm·a^-1．CRS模式得到 百年来网湖沉积速率变化较大，20世纪50年代以前，平均沉积速率为0．2cm·a^-1左右；50年代至80年代中期，平均沉积速率上了一个台阶，约为 0．4cm·a^-1；80年代中期以后平均沉积速率攀升至约0．6cm·a^-1，网湖沉积速率变化与湖区自然环境的改变和人类活动的影响密切相关． . 采用放射性核素^137Cs和^210Pb计年法测定百年来湖北网湖沉积物的年代，据此计算 出网湖的沉积速率．结果表明：2种计年方法测得的沉积速率基本一致，以1954年和1963年为时标，^137Cs测得的沉积速率分别为 0．594cm·a^-1和0．557cm·a^-1。^210Pb计年法CIC模式计算得到网湖平均沉积速率为0．56cm·a^-1．CRS模式得到 百年来网湖沉积速率变化较大，20世纪50年代以前，平均沉积速率为0．2cm·a^-1左右；50年代至80年代中期，平均沉积速率上了一个台阶，约为 0．4cm·a^-1；80年代中期以后平均沉积速率攀升至约0．6cm·a^-1，网湖沉积速率变化与湖区自然环境的改变和人类活动的影响密切相关． |
| [26] | . 采用放射性核素210Pb和137Cs计年方法,建立了长江中游网湖近代沉积物的年代序列,并对网湖沉积物的粒度组成、磁性参数、重金属元素、花粉组合以及营养盐含量等指标进行了分析。根据沉积指标垂直分布的综合特征,结合湖区史料,重建了网湖100年来沉积环境的演变过程。通过对沉积指标与湖区人口变化、工农业产值等数据的比对,发现中华人民共和国成立以后沉积物中TOC和TN浓度与人口变化存在较高的相关性,相关系数分别达到0.8892和0.8928(P0.001);沉积物中重金属元素富集序列、营养盐富集序列与孢粉含量的变化序列与湖区人类活动具有较好的耦合性。表明网湖沉积指标可以敏感地反映湖区的人类活动。 . 采用放射性核素210Pb和137Cs计年方法,建立了长江中游网湖近代沉积物的年代序列,并对网湖沉积物的粒度组成、磁性参数、重金属元素、花粉组合以及营养盐含量等指标进行了分析。根据沉积指标垂直分布的综合特征,结合湖区史料,重建了网湖100年来沉积环境的演变过程。通过对沉积指标与湖区人口变化、工农业产值等数据的比对,发现中华人民共和国成立以后沉积物中TOC和TN浓度与人口变化存在较高的相关性,相关系数分别达到0.8892和0.8928(P0.001);沉积物中重金属元素富集序列、营养盐富集序列与孢粉含量的变化序列与湖区人类活动具有较好的耦合性。表明网湖沉积指标可以敏感地反映湖区的人类活动。 |
| [27] | . Observations have been made during five years on the fluctuations in the numbers of Asterionella formosa and other plankton diatoms, and in the concentrations of dissolved silica, nitrates and phosphates in four bodies of water in the English Lake District. This account refers mainly to the period from winter to summer. The close of the spring period of increase of Asterionella is not directly due to light or temperature. Loss of cells by floods is more or less compensated for by the replenishment of the lake with nutrients in the inflow water. Grazing by animals has no appreciable effect on the fluctuations in numbers. Fungal parasitism may affect the course of the spring increase in numbers, but is rarely the cause of its end. Very rarely, depression of the numbers of Asterionella by parasitism may lead to other diatoms becoming dominant and utilizing the available nutrients (e.g. silica). The close of the spring period of increasing numbers of Asterionella is frequently due to depletion of the available silica. Confirmation is deduced for Pearsall's (1932) view that diatoms cannot multiply to any marked extent when the concentration of silica is less than 0.5 mg. per litre. The supply of available silica does not provide a complete explanation of the fluctuations in diatom numbers in all the lakes considered or at all times of year. The mean silica content of the cells of Asterionella formosa is 140 g. per million. Confirmation has been obtained for the view of Einsele & Grim (1938) that the amount of silica per unit area of cell is constant under all conditions. The nitrogen content in natural and cultural populations varied from 6 to 12 g. per million cells (mean value 8 g.). The phosphorus content, by contrast with silica and nitrogen, varied widely in natural and cultural populations (0.06-4.2 g. per million cells). The cells of Asterionella can store phosphorus in excess of immediate requirements and when the concentration in the water is 1 g. per litre or less. Asterionella can utilize calcium at a concentration of 400 g. per litre, a lower concentration than occurs in any lake in the English Lake District. Reasons are given for the view that the supplies of nitrogen, phosphorus, carbon and calcium appear to be sufficient to support larger populations of Asterionella than are observed during the period under review. Little or nothing is known concerning the importance of any other substances in the lake waters. Limitation of growth due to lack of silica shows a difference from that due to lack of light. The present observations and conclusions are discussed in relation to those for other lakes made by the author and other workers. It is emphasized that every algal species and lake must be considered separately. |
| [28] | . Knowledge of the composition and ecological preferences of diatom assemblages in northern regions is important for paleoenvironmental reconstructions of variables related to climate and/or anthropogenic disturbances. Relatively little is presently known about diatoms from circumpolar treeline areas, especially for lakes located in northern Russia. Our study set included lakes in the Siberian tundra, forest-tundra, and boreal forest regions close to Norilsk, of which nine sites were subject to anthropogenic disturbances, such as mining and housing developments. We enumerated surficial sediment diatom assemblages and used multivariate statistical techniques to investigate which environmental variables were important in explaining the variation in diatom assemblages within our lake set. Deeper lakes were associated with higher abundances of planktonic centric taxa, such as Cyclotella K tzing species. Warmer, higher conductivity forested lakes were associated with higher abundances of planktonic pennate taxa, such as Fragilaria nanana Lange-Bertalot. Diatom assemblages in the colder tundra lakes were significantly different from those in forested regions, and were dominated by small benthic Fragilaria Lyngbye species. Disturbed lakes near the Norilsk smelters exhibited slightly higher metal (Cu) concentrations and conductivities, and were associated with pollution-tolerant Nitzschia Hassall taxa, as well as species associated with higher electrolyte concentrations, such as Navicula capitata Ehrenberg. However, in comparison with diatom assemblages from other regions of intense mining (e.g. Sudbury, Canada), the assemblages appear relatively unaffected by mining activities, most likely reflecting the suppression of aqueous metal concentrations due to the alkaline nature of these lakes. Overall, diatom assemblages were very similar to those found in northern Canadian and Fennoscandian lakes, suggesting mat the Siberian taxa are representative of a circumpolar arctic diatom flora. |
| [29] | . |
| [30] | . 中国科学院机构知识库(中国科学院机构知识库网格（CAS IR GRID）)以发展机构知识能力和知识管理能力为目标，快速实现对本机构知识资产的收集、长期保存、合理传播利用，积极建设对知识内容进行捕获、转化、传播、利用和审计的能力，逐步建设包括知识内容分析、关系分析和能力审计在内的知识服务能力，开展综合知识管理。 |
| [31] | . We compared the benthic diatom composition of lakes, and lake inlet and outlet streams in a high elevation catchment (~2600 m a.s.l.). The catchment was separated in a southern and northern basin with different water sources. Streams in both basins flowed through a series of small lakes before converging into a lake with a primary outlet. The south basin had lower water temperatures and 2 higher nitrate-N levels (up to 300 g/L) while the north basin had 2-4 higher levels of particulate-P, particulate-N, and particulate organic matter. 143 and 109 diatom species was identified in streams and lakes, respectively, with a similar number of species found in each basin. PCA showed a clear separation between basins. Of the 10 most common species, Psammothidium helveticum, Achnanthes helvetica var. minor, Achnanthes marginulata, Achnanthes subatomoides, and Diatoma mesodon were more abundant in south basin, whereas Achnanthidium minutissimum, Aulacoseira alpigena and Luticola goeppertiana were more abundant in the north. In general, lake outlet assemblages were similar to respective downstream lake inlet assemblages. Composition shifted along each basins longitudinal flow path. The spatial patterns in species composition reflected the hierarchical interaction of landscape features (geology, hydrology) on longitudinal gradients (lake position) in the stream/lake network. |
| [32] | . . |
| [33] | . 依据沉积物钻孔的高分辨率硅藻研究,利用长江中下游现代湖泊硅藻与总磷转换函数结果,定量重建了太白湖400余年来古湖水总磷浓度的变化.结果表明,约1630 AD前和1800-1924 AD期间,湖水总磷浓度较低,在50-68μg/L之间;1630-1800 AD,总磷浓度偏高,总体上在50-160μg/L之间变化,变幅较大.1800-1924AD,总磷浓度明显下降为谷值段,且变化相对稳定(50μg/L左右);1924-1953AD,总磷浓度仍较低,但有增加趋势(50-63 μg/L);20世纪50年代开始,总磷浓度出现快速增加;至1970年后,总磷浓度超过120μg/L左右.利用样品相似对比的方法发现约80%的样品具有较好的重建效果.古湖水总磷浓度值的变化揭示了该湖两次明显的富营养化过程,初步探讨了其驱动机制.根据重建结果提出:太白湖自然营养本底总磷值约为50μg/L左右,可作为该湖治理时的参考目标. . 依据沉积物钻孔的高分辨率硅藻研究,利用长江中下游现代湖泊硅藻与总磷转换函数结果,定量重建了太白湖400余年来古湖水总磷浓度的变化.结果表明,约1630 AD前和1800-1924 AD期间,湖水总磷浓度较低,在50-68μg/L之间;1630-1800 AD,总磷浓度偏高,总体上在50-160μg/L之间变化,变幅较大.1800-1924AD,总磷浓度明显下降为谷值段,且变化相对稳定(50μg/L左右);1924-1953AD,总磷浓度仍较低,但有增加趋势(50-63 μg/L);20世纪50年代开始,总磷浓度出现快速增加;至1970年后,总磷浓度超过120μg/L左右.利用样品相似对比的方法发现约80%的样品具有较好的重建效果.古湖水总磷浓度值的变化揭示了该湖两次明显的富营养化过程,初步探讨了其驱动机制.根据重建结果提出:太白湖自然营养本底总磷值约为50μg/L左右,可作为该湖治理时的参考目标. |
| [34] | . Diatoms are used widely for paleolimnological studies in lakes, but their use for studying the environmental history of reservoirs has not been tested extensively. Reservoirs have hydrodynamic characteristics intermediate between those of rivers and lakes. This study assessed the utility of diatom assemblages as recorders of long-term changes in hydrodynamics and spatial gradients in Liuxihe Reservoir, an impoundment in southern China. Four sediment cores were collected in the reservoir, from the riverine, transition and lacustrine zones. Each core was sectioned at 2-cm intervals to investigate the stratigraphic distribution of accumulated diatoms. Varve counting was used to develop a chronology for one of the cores. The unique characteristics of Liuxihe Reservoir, including its large size, great depth, long narrow morphology and strong thermal stratification for 10 months of the year, limit secondary sedimentation processes and preserve the varves, enabling development of an accurate chronology. Damming profoundly altered the physical environment of the former river, especially in the lacustrine zone, where the change is clearly illustrated by diatoms in the sediment. Diatom abundance increased as a consequence of nutrient enrichment after construction of the dam in 1958, but later decreased as the new impoundment stabilized. After damming, relative abundance of Cyclotella increased along with a simultaneous decrease of Navicula and Achnanthes in the lacustrine zone, most significantly in 1963, when Cyclotella replaced Navicula as the dominant genus. This switch was indicative of a general shift from a lotic to a lentic habitat. A longitudinal gradient was apparent in the patterns of sedimentation and diatom accumulation at different sites in the reservoir, with diatom abundance highest in the transition zone. In the long term, water discharge from the reservoir showed a weak, but significant negative correlation with diatom abundance in the lacustrine zone ( r = 0.320, P = 0.03). In summary, diatom assemblages in the Liuxihe Reservoir sediments recorded past changes in hydrodynamics, suggesting that paleolimnological study of some impoundments is feasible. |
| [35] | . The conversion of much of the earth's land surface to agriculture or urban land has had major effects on nutrient flows from the local to the global scales. Natural ecosystems generally conserve nutrients and store organic matter effectively. In all agricultural |
| [36] | . The Yangtze floodplain is characterized by numerous large (surface area > 1 km2; 09080425% are > 10 km2) and shallow lakes (maximum depth mainly < 5 m). Floodplain lakes are inherently dynamic and important sites for biogeochemical cycling, biodiversity as well as human resources. Importantly, the degree of hydrological connectivity between lakes and river channels is affected by climate, geomorphic processes as well as cultural disturbance of the catchment. This study investigated the long-term (090804200 years) interaction between a shallow floodplain lake (Taibai Lake; area 25 km2, mean depth 300·2 m) and the Yangtze River using high-resolution multi-proxy analysis (diatoms, geochemistry, and grain size) of a 210Pb-dated sediment core. Diatom assemblages in Taibai Lake exhibited a strong temporal succession and were successively dominated by Aulacoseira granulata (planktonic), Gyrosigma acuminatum (periphytic), and the facultatively planktonic Nitzschia palea over the past 200 years. Eutrophication as inferred by diatom inferred-total phosphorous (DI-TP), however, only started around 1990 with TP concentration increasing from 65 to 95 0008g L0908081. Prior to 1950 DI-TP was constant and detrended correspondence analysis axis 1 sample scores (of the diatom assemblages) were not correlated with DI-TP concentration suggesting that there were other stressors driving changes in the diatom assemblage besides nutrients. We used sediment grain size as a proxy for hydrological connectivity; median grain size is strongly correlated with the abundance of A. granulata (R2 = 000·67). A comparison of the diatom stratigraphy with physical and geochemical proxies suggested that Taibai Lake shifted from a riverine-influenced, turbid algae-macrophyte mixed state to a clearwater macrophyte-dominated state around 1950 AD, primarily due to the changes in the hydrological regime of the floodplain resulting from land reclamation and building of reservoirs. After 1990 AD, the lake ecosystem deteriorated following continuous input of nutrients from agriculture and aquaculture, shifting to a hyper-eutrophic algae-dominated state. These results indicate the dynamic nature of floodplain ecosystems and the complexity of multiple stressors affecting them over decadal timescales and the long-term interaction between anthropogenic and natural forcing processes. Copyright 0008 2011 John Wiley & Sons, Ltd. |
| [37] | . 在对长江中下游地区45个湖泊表层沉积硅藻属种分布及多次季节性水样调查的基础上,研究了57个常见硅藻属种对总磷指标的生态学特征.利用加权平均回归方法,计算出常见属种对总磷指标响应的生态最佳值及忍耐幅度.根据生态学理论得出,属种Cyclotellameneghiniana、C.atomus、Stephanodiscusparvus、S.minutulus、Naviculasubminiscula是长江中下游湖泊富营养化发生的很好的指示性属种;而Aulacoseiraalpigea、Cyclostephanosdubius、C.tholiformis、C.invisitatus、Stephanodi . 在对长江中下游地区45个湖泊表层沉积硅藻属种分布及多次季节性水样调查的基础上,研究了57个常见硅藻属种对总磷指标的生态学特征.利用加权平均回归方法,计算出常见属种对总磷指标响应的生态最佳值及忍耐幅度.根据生态学理论得出,属种Cyclotellameneghiniana、C.atomus、Stephanodiscusparvus、S.minutulus、Naviculasubminiscula是长江中下游湖泊富营养化发生的很好的指示性属种;而Aulacoseiraalpigea、Cyclostephanosdubius、C.tholiformis、C.invisitatus、Stephanodi |
